Art of cracking hydrocarbons



April 8', 1930. E. w. ISOM 1,753,432

ART OF [CRACKING HYDROCARBONS' Filed May 25, 1927 2 sheets-sheet 1 7a Condenser Fer/rru/af/ny Men 115 INVENTOR Edward W Isom ATTO A ril 8, 1930. E w, 150M 1,753,432

ART OF CRACKING HYDROCARBONS fire-Box T u W INVENTOR Edward W-Isom Patented Apr. 8, 1930 UNITED STATES PATENT OFFICE EDWARD W. ISOM, OI SCAR-SDAL E, NEW YORK, ASSIGNOR TO SINCLAIR REFINING COM- PANY, OF NEW YORK, N. Y.,

A CORPORATION OF MAINE ART OF CRACKING HYDROCARBONS Application filed May 25,

This invention relates to improvements in the cracking of heavier and higher boiling hydrocarbon oils, such as fuel oil, gas oil and kerosene, to produce lighter and lower boiling hydrocarbon oils, such as gasoline or gasoline-containing cracked distillates. The heat for such operations is commonly supplied by passing hot products of combustion from a firebox over tubes or pipes through which the oil is circulated and in which it is heated'to a crackin temperature. This invention relates particularly to improvements in supplying heat for such operations.

'The products of cracking operations usually include, in addition to the desired lighter danger of burning or rupturing the tubes or pipes. The tendency toward overheating, moreover, is cumulative since local overheating tends to cause excessive local decompos1- tion with the formation and tendency to deposit of excessive amounts of pitchy and carbonaceous materials. Such difficulties can be overcome in an advantageous way by recirculating over the heating tubes or pipes in admixture with fresh hot products of combustion a portion of the heating gases which have passed over the heating tubes or pipes. Such recirculation of a portion of the heating gases has numerous advantages. For example, the volume of heating gases passing 'overthe heating tubes or pipes is increased and the consequent increase in velocity improves the rate and efficiency of heat transfer, the tempering action of the recirculated heating gases assists in protecting the tubes'or pipes and also makes it possible to carry out combustion of the fuel used at much higher tem- 1927. Serial No. 194,002.

1piieratures with consequent greater fuel efciency than otherwise would be possible without danger of overheating the tubes or pipes or of local overheating, and better distribution of the heat absorption through the tubes or pipes is made possible, without decreasing but rather increasing the general efficiency' of the heating operation.

However, as an increasing proportion of the heatin gases which have passed over the heating tu es or pipes is recirculated thereover, there is an accompanying approach of the temperature at which the mixture of heating gases first contacts with the heating tubes or pipes and that at which it leaves the heating tubes or pipes. As an increasing proportion of the heating gases is recirculated, the temperature at which the mixture of heating gases first contacts with the heating tubes or pipes decreases and that at which it leaves the heating tubes or pipes tends to increase.

According to the present invention, the heating gases including the hot products of combustion from the firebox are passed over heating tubes or pipes through which a stream of oil undergoing cracking is circulated so that the temperature of the mixture of heating gases is progressively reduced, heatin gases for recirculation over the heating tu es or pipes with which the fresh hot products of combustion from the furnace first heating gases which have passed over oil heating tubes or pipes and the temperature of which has been thereby reduced are socured, and at the same time a further improvement in efiiciency and economy is effected by further reduction of the temperature at which the heating gases not recirculated ai'e discharged. While the volume of heating gases passing over the heating tubes or pipes beyond the point at which a por-- tion of the heating gases are withdrawn for recirculation'may not be increased, these further heating tubes or pipes are protected from overheating since the temperature at which the heating gases first contact with these further heating tubes or pipes is not greater than that of the heating gases pass. ing over the heating tubes or pipes closer, in the passage of the heating gases, to the firebox and-over which a portion of the heating gases is recirculated.

The invention will be further described in connection with the accompanying drawings which illustrate diagrammatically and conventionally, two forms of apparatus embodying the invention and adapted for carrying out the invention, but it will be understood that this further description and illustration of the invention is intended for exemplificationand that the invention is not limited thereto. In the drawings, Fig. 1 illustrates the invention as applied to one form of cracking system, and Fig. 2 illustrates the invention as it is applied to another form of cracking system.

The apparatus illustrated in Fig. 1 co nprises a single pass heater discharging lnto 'a shell 3. The shell '3 is arranged on a furnace setting 4 by which external heat may be supplied thereto, or the shell 3 may be heated internally only by the hot oil products discharged into it from the single pass heater. Liquid residues may be discharged from the shell 3 through connection 5. Vapors from the shell 3 pass successively through the reflux condensers 6 and 7 and from the latter to a condenser (not shown) in which the cracked distillate product is condensed. Fresh oil may be supplied to the shell 3 from tank 8. This fresh oil may be passed in heat exchanging relation with the vapors flowing through the reflux condensers 6 and 7 on its way to the shell 3, thereby being preheated and serving to cool and reflux the vapors. Additional refluxing may be effected by passing an additional amount of such fresh oil through the reflux condensers and discharging it through connection 9. Reflux condensate from the reflux condensers 6 and 7 passes to tank 10, or part of the reflux condensate from reflux condenser 6 may be returned to the shell 3 through connection 11.

A super-atmospheric pressure may be maintained in the shell 3 by means of valve 12 and the reflux condensers 6 and 7 operated at atmospheric pressure or at an intermediate pressure, or the same pressure may be maintained on the shell 3 through the reflux condensers 6 and 7 by means of valve 13. Likewise, the final condenser (not shown) may be operated at the same pressure as that prevailing throughout the system, or at atmospheric pressure, or at an intermediate pressure. Reflux condensate from tank 10 is forced through the single pass heater by means of.

condense and reflux those constituents of the.

vapors heavier or higher boiling than are de sired in the product. A pressure up to 100 pounds per square inch or higher pressure, may be maintained in the shell 3 and oil supplied to the single pass heater under pressure just sufficient to effect discharge of the hot oil products therefrom into the shell 3, or ahigher pressure may be used in the single pass heater and this pressure reduced by means of valve 16. The hot oil products may be discharged from the single pass heater at a temperature in the neighborhood of 800 F. to 1,200 F. and a temperature in the shell may be maintained in the neighborhood of 700 F to 850 F. The charge of oil in the shell 3 may be run substantially to coke or a coke-like residue, or the operation may be conducted in a continuous manner by discharging continuously or at regular intervals tar or pitchla-den oil through connection 5.

In this apparatus, the present invention is illustrated as applied to the single pass heater. This single pass heater comprises a furnace 20 in which a number of heating tubes connected to form a continuous heating coil 21 are arranged. Oil is supplied to the heating tubes through connection 22 and the hot oil products are discharged-there-' from through connection 23. The heating furnace 20 is provided with a firebox 24 and a stack flue 25, heating gases being circulated from the firebox over the oil heating tubes in the furnace of the stack flue. The firebox is provided with suitable means for burning the fuel employed to supply the heat used in the cracking operation. Before the hot products of combustion from the firebox 24 come in contact with the oil heating tubes,

by admixture therewith before the mixtureis contacted with the oil heating tubes. Connection 26 is provided for this recirculation of heating gases. This return connection includes a blower which may be operated by a steam jet 27, as illustrated, or by other suitable means for maintaining circulation of the returned recirculated heating gases.

In place of the blower illustrated, a fan or other suitableforcing means may be used. This recirculating connection 36 is arranged, as illustrated, at a point such that the heating gases withdrawn therethrough pass over a part but not all of the heating tubes. The

remaining heating gases, not withdrawn through connection 26, continue in passage over the remaining heating'tubes and are discharged, after further reduction in temperature, through stack flue 25. The oil heating tubes are thus protected, and the improvements in efliciency and economy accompanying recirculation of a portion of the heating gases are secured, the temperature of combustion in the firebox may be regulated ture is discharged through connection 32 to a suitable fractionating or. condensing system. Oil is forced through the heating coils bymeans of one or more of the pumps 33, 34 and 35. The'heating coils are arranged in successive heating flues in the furnace, A, B, C and D, and the general flow of oil is successively through the heating coil in flue A then through that in flue B, and then through that influe C, being discharged to the vaporizing'drum from the last through connection 36. Before entering the heating coil in flue A, fresh oil may be passed through the heating coil in flue D. Pumps 34 and35 are arranged to supply fresh oil at intermediate points in the passage of the oil through the heating coils. Reflux condensate or heavier or higher boiling fractions separated from the vapors discharged from the connection 32, may be supplied to one or more of the pumps 33, 34 and 35 together with fresh oil. A superatmospheric pressure may be maintained in the heating coils and regulatedb y means of valve 37. The vaporizing drum 30 may be operated substantially at atmospheric pressure or at a pressure intermediate that andthe pressure at which the hot oil products from the heating coils are discharged through connection 36. Pressure in the vaporizing drum 30 may be maintained and regulated by means of valves 38 and 39.

In operation to produce gasoline or a gasoline-containing distillate, the gasoline character stock may be supplied to pump 33.

and gas oil character stocks may be supplied to the pumps 34 and 35. The stock discharged from pump 33 may be forced directly through the heating coil in flue A, or it ma be passed or part1 passed first through the heating coil in ue D, by appropriate regulation of the Valves illustrated. Pressures in the neighborhood of 100 pounds to 300 pounds per square inch or higher pressures maybe maintained in the heating coils. The hot oil products may be discharged from the heating coils at a temperature in the neighborhood of 700 F. to 900 F.

In this apparatus, the successive heating coils are arranged in a series of flues .A, B, C and D in the heating furnace 40. This heating furnace is provided with a firebox 41 and a stack flue 42, heating gases being circulated from the firebox successively through the flues A, B, C and D, and over the heating coils therein, to the stack flue. The firebox 41 is provided with suitable means for burning the fuel employed to supplythe heat used in the cracking operation. As the mixture of heating gases, including fresh hot products of combustion from the firebox, flow through the successive flues in the heating furnace, its temperature is progressively reduced. Before the fresh hot products of combustion from the firebox 41 come in contact with the heating coil in flue A, they are admixed witha portion of the heating gases which have passed through flue A the temperature of which has been accordingly lowered by the heat absorbed in the heating coil therein. The connection 43 is provided foreflt'ecting this recirculation of heating gases which have passed over the heating coil in flue A. This return connection includes suitable forcing means as previously described. The recir culated heating gases are discharged through outlet 44 where they mix with the fresh hot products of combustion from the firebox before the latter contact with the heating coil in flue A. These recirculated heating gases are withdrawn adjacent the connection between flueA and flue B, throu h the inlet 45 to the return connection. T e remaining heating gases then pass in succession over the heating coils in flue B, in flue C and in flue D, finally being discharged through the stack flue at a temperature much lower than that at which they escape from flue A or enter flue B.

I claim:

1. In cracking hydrocarbon oils in operations in which a flowing stream of oil is heated to a cracking temperature by heat exchange with hot products of combustion from a firebox in which fuel is burned, the imof oil through a heating conduit and passing heating gases including hot products of combustion from a firebox in heat exchanging relation therewith whereby the oil is heated to a cracking temperature and the temperature of the heating gases is progresisvely reduced, withdrawing a portion of the'heating gases from an intermediate point in the passage of the heating gases over the heating conduit at an intermediatetemperature, recycling such withdrawn heating gases over the heating conduit in admixture with fresh hotproducts 5 of combustion from the firebox, and discharging the remaining portion of the heating gases after further passage over the heating conduit and at a lower temperature than that at which the recycled heating gases are with- 10 drawn.

2. In apparatus for cracking hydrocarbon oils, a heating furnace having a firebox and a stack flue and heating fiues connecting the firebox with the stack flue, oil heating tubes 15 arranged in said heating flues and means and connections for circulating oil there through, a return flue communicating at one end with said heating flues at a point intermediate the positions of said oil heating tubes nearest the 20 firebox and those nearest the stack flue and at the other end with a heating flue nearer the firebox, and forcing means in said return flue for recirculating through said flue nearer the firebox heating gases withdrawn :Erom' the g5 heating flues at said intermediate points.

In testimony whereof, I have subscribed my name.

EDWARD W. ISOM. 

